Fluid blast circuit interrupter



March 8, 1960 v. E. PHILLIPS FLUID BLAST CIRCUIT INTERRUP'TER Filed April 150, 1958 w M N)- n Jill! M., @4 mmm .J 4 l 9 hn! wv u a ne. H w f n n .d ww n M. w n m wo m m. m K s l z P H m m Iventor: Vrgel E. phillips,

` His Attorney.

,Hur pilaar 2,927,986 FLUD BLAST CIRCUIT INTERRUPTER Virgel E. Phillips, Springfield, Pa., assignor to General Electric Company, a corporation of New York Application April 30, 1958, Serial No. 732,084

6 Claims. (Cl. 200-150) This invention relates to an electric circuit interrupter of the fluid-blast type and, more particularly, relates to an interrupter of this -type which relies upon pressure responsive valve means for controlling the flow of exhaust iluids through its exhaust passages during and immediately following circuit interruption.

For improving the abil-ity of a uidblast circuit interrupter to successfully interrupt low currents, it has been proposed heretofore that the normal exhaust passages of the interrupter be provided with one or more pressureresponsive valves. During low current interruptions, these valves act to severely restrict the exhaust passages andthus act to increase the pressures developed within the interrupter, as compared to those pressures developed without thel valves. These increased pressure-s have considerably improved the interrupting ability of the interrupter in the low current range, especially with regard to those low current arcs which generate only small amounts of gases. l

For high current interruptions, however, much larger quantities of gases are generated, and these gases tend to create very high pressures within the interrupter. The extent of the pressure build-up is limited by the fact that these valves controlling the normal exhaust passages of the interrupter open when the pressure exceeds a predetermined value. But for extreme high current interruptions, these exhaust valves have no-t ybeen capable of adequately limiting the pressures developed.

It is therefore an object of the present invention to provide improved means for limiting to safe levels the pressures developed within such an interrupter during extreme high current interruptions.

After a high current interruption and as soon as the pressure within `the interrupter has fallen below a predetermined value, fa pump, usually provided for this purpose, automatically operates to force fresh insulating Huid through the interrupter so as to scavenge the interrupter of arcing products. It is highly desirable .that this scavenging action take place through those particular exhaust passages which had been relied upon for the venting of gases during interruption, since it is here that the arcing gases are more likely to have been left behind or trapped. This is pointed out in application S.N. 717,892, Schneider, filed February 27, 1958, and assigned to the assignee of the present invention, which discloses and claims exhaust valves which are adapted to facilitate this desired scavenging of the normal exhaust passages. I-t is, of course, important that any added pressure-limiting means included in the interrupter not interfere -with this desired scavenging pattern.

Accordingly, another object of my invention is to incorporate pressure limiting means in such an interrupter in such a manner that the pressure-limiting means does not interfere with the desired scavenging pattern. An additional object is to attain this latter result even though the pressure limiting means is constructed Vto become effective at pressures below those required to initiate openingcf the pressure-responsive-exhaust valves.

2,927 ,986 Y hater-ned Mar. s, 1960 In applying my invention to a liquid-lilled interrupter having pressure-responsive exhaust valves controlling its normal exhaust passages, I provide the interrupter with a pressure-responsive relief valve, in addition to the exhaust valves. This relief valve is set to open at a pressure not substantially exceeding and preferably below the pressure required to initiate opening of the exhaust valves. ln addition, ythe relief valve is located at a point so remote from any arcing region of the interrupter that substantially only liquid, and no significant amount of gas, is forced ytherethrough during the time required for the exhaust valves to open during interruption. As liquid leaves the interrupter through the relief valve, an added portion of the interrupters volume is made available for arc-generated gases. The gases generated during the early stages of interruption ll -this newly-available vol-- urne and subsequently act as a pressure-limiting cushiorr for protecting the interrupter, say, on a succeeding half-- cycle when the highest pressures normally occur.

In accordance with another aspect of my invention, the pressure-responsive exhaust valves are so constructed that they will be held open by pressures within the interrupter below the value required to initiate their opening. They will also be held open by pressures against which the relief valve is capable of closing, even though the relief valve might open at a lower pressure than that required to initiate opening of the exhaust valves. Operation of the scavenging pump after the exhaust valves have been opened create sufficient pressures to hold the exhaustv valves open but not enough to hold the relief valve open. The relief valve therefore closes during scavenging and thus allows most of the scavenging action to take place through the passages leading to the exhaust val-ve, where scavenging is most needed.

For a better understanding of my invention, reference'V may be had to the following description taken in connec-` tion with the accompanying drawing, wherein:

Fig. l is a side elevational view partly in section show-` ing an interrupter embodying one form of the present in` valve, for use with an interrupter such as shown in Fig. 1. Referring now to Fig. 1, the interrupter 1 shown therein is of the general type described and claimed in Patent No. 2,749,412, McBride et al., assigned to the assignee of the present invention. This interrupter 1 is mounted, ,along with another similar interrupter (not shown) inside a relatively large oil-iilled enclosing tank. The two interrupters are electrically connected by a recip rocable blade contact 2 of conventional form, such as shown for example iny U.S. Patent 1,548,799, Hilliard, assigned to the assignee of the present invention.

The interrupter 1 is supported within the `oil-iilled tank from an insulating bushing structure 3 having a conductor stud to which an adapter 4 is suitably secured in a known manner. Adapter 4 is arranged to cooperate with suitable tie bolts (not shown) which structurally interconnect the interrupter unit 1 andthe adapter 4.

The interrupter 1 comprises a .tubular insulating casing '5 enclosing a pluralityof pairs 8, 9 of separable interrupting contacts which are electrically connected in series.

l10 is preferably of the conventional cluster-type comprising a plurality of fingers urged radially inwardly by suitably resilient means (not shown). In a corresponding manner, the lower pair 9 of contacts comprises a similar fixed contact assembly 12 and a relatively movable contact 13. The pairs of interrupting contacts S and9 are electrically connected in series by means of suitabie current transfer contacts 14 andthe transverse- 1yextending contact support casting 15. For supporting the movable contacts 11 and 13 and for interrelating them for simultaneous movement so as to draw a pair ofsimultaneoitaly-occurring arcs, there is provided a common crosshead 16 of conducting material to which the lower rod Contact 13 is directly secured and to which the upper rod contact l1V is suitably fixed by means of an interconnecting insulating rod 17.

.in order to complete the electrical circuit through the interrupter and to provide an isolating contact arrangement for the interrupter, therel is provided on the crosshead 16 an external contact button 13 which cooperates with an isolating Contact 1% secured to the movable switch blade 2 to form a pair of isolating contacts. From the above description, it will be apparent that the electrical circuit through the interruptor extends from the adapter 4 through the conductor 20, through the upper interrupting contacts 10, 11, through the current transfer contacts 14 and the casting 1S, then through the lower interrupting contacts 12, 13, the crosshead 16, the contact button 18, the isolating contact 19, and finally through the switch blade 2 and tothe cooperating interrupter (not shown), which is disposed at the opposite end of the switch blade 2.

A circuitfopening operation is produced by driving the switch blade 2 rapidly downward. This allows suitable compression springs 6 to force the crosshead 16y together with the contacts 11 and 13 rapidly downward so as to draw a pair of circuit-interrupting arcs in the regions where these contacts part from their mating stationary contacts. After a predetermined downward movement, the crosshead 16 is blocked by suitable stop means (not shown) from following the` switch blade 2. The switch blade 2, however, continues moving downwardly and, as a result, establishes an isolating break between the contacts 1S and 19 in a conventional manner.

The. Compression springs 6,v it will be noted,v bear at their upper end against a stationary plate 7. This platev 7 and the adapter 4 act to enclose the interior of the interrupter 1 at its respective lower and upper ends.

Adjacent to the serially-related interrupting contacts 8 and 9 are a pair of arc-extinguishing; units inithe form,

of bathel stacks 21 and 22. Baie stack 21 is formedof a plurality of superposed. apertured baie plates 23k of insulating material which together providea central interrupting passageway 24. and a plurality of verticallyspaced, angularly-aligned exhaust passages 25 radiating therefrom. The exhaust passages are preferably formed by slotting cer-tain of thebafe plates 23 in a. well-known manner. When a high current are is,v drawn within the passageway 24.in responseA to` separation of contacts 1.0 and 1.1, pressure is produced within the oil-filled casingand is effective to force a highly concentrated blast of dielectric iiuid` across, the arc through theV slots or exhaustpassages. and out the registering` exhaust port 26fformed in the adjacent wall of casing* 5. blast action will be described' in. greater detail hereinafter. The lower baffle stack` 22 generally corresponds toY the baille, stack 21 except. that` battle stack 22 isY provided with an opening. 27vthroughwhich reciprocates the insulating. nortionof the` upper rod Contact 11.

For controlling. theflow.v of uid through the exhaust passages. 25, 26, there is provided aA pressure-responsive exhaust valve 100 for each of the arc extinguishing units 21 and 22. These exhaust valves are preferably con structed as describedand claimed' in the aforementiouedV application S.N. 717,892, Schneider, assigned to the assignee of the present invention. Referring to Figs. 2 and 3, each of these exhaust valves comprises a tubular valve body 102 which is suitably clamped to the casing 5, as by means of a nut 104 on `the exterior of the tubular body 102. When the nut 104 is tightened, it acts through a washer 108 to force a shoulder 106 formed on the tubular housing 162 into clamping engagement with a recessed portion 107 formed in the interior of casing 5. n

For controlling the flow of fluid through the hollow valve body, there is disposed therewithin a pivotallymountedvalve member in the form of a metallic vane or iiapper 110. This vane 11i) is fixed to a pivotally mounted shaft 112 which extends horizontally across the bore of the valve body at an off center location, which, in Fig. l, is shown as being closer to the bottom inner surface of the valve body than to the top inner surface. Preferably, the shaft 112 is of a rectangular cross section, and the shaft-receiving opening in the valve member is of a similar shape so as to preclude relative rotation between these parts. For providing smooth bearing surfaces for rotatably supporting the shaft 112, on the valve body 102 two sleeves 113 are fitted about opposite ends of the shaft 112. Each of these sleeves 113 is anchored to the shaft for rotation therewith and has a cylindrical outer periphery journaled in a suitable openingA 114 in the valve body 110. These sleeves` 113 allow the shaft 112 to rotate freely within the openings 114.

Located externally of the valve body 102 are crank arms 115 which are suitably fastened to the shaft 112 at opposite ends thereof. In this regard,` each of, these crank arms is preferably welded' or otherwise attachedto an adjacent sleeve 113 and each arm is preventedY from shifting axially of the shaft 112 by means of a nut 115er suitably threaded on each end of the shaft.

The vane 11-3 is urged into its closed position of Fig. 3 by means of a tension spring 116 which interconnects the outer ends of the crankl arms 115. Thisv tension spring 116 extends about the top exterior of the valve body 1012 and is suitably anchored to the valve body 102 adjacent the top surface of the valve body. The means for anchoring the spring 116 to the valve body preferably comprises a lug 1,18, which is fastened to, the

valve body 102, as by screws 119. The lug: comprises a curved ange 120 extending about` a portion` of the spring periphery, as shownin Fig. 3, and thereby preventing movement of the top portion-of thespring 116 axially along the valve body 102..

When the pressure within the intermpter exceeds a predetermined value, it` forces the valve member 110 counterclockwise about they axis of pivot shaft 112 thereby opening the central exhaust passageway through the valve body 102 and allowing uid to ow therethrough. As will soon be pointed out more clearly, the resilient means 115, 116 exerts a generally decreasing force onv the valve member 110 as it travels away from its closed position toward its fully-open position. This follows` from the fact that the effective moment arm through which tension spring 116 acts on the vane 110- becomes progressively smaller as the vane 110 moves from its closed positiontoward its fully open position. Thisrnoment arm is the effective. distance between the axis of the shaft i112 and a plane n containing the linesv of action.

of the tension spring, this distance being measured normal to the plane n. This moment arm is represented at m in Fig. 3. As the vane moves towards its open position, the plane n approaches the axis of shaft112, or stated otherwise, approaches an in-line position relative to the crank 115, and the moment arm m accordingly decreases. In the disclosed valve, this decreasing moment arm more than offsets the increasing force resultingV from lengthening of the tension spring, and,l accordingly, the net or effective,springiclosing forceonthe vane. generallydecreases as4 the. vanemovesfrom its closed to itsifully,-

ansiosa open position. This decreasing effective force relationship is occasionally referred to hereinafter as the negative gradient characteristic of the valve. The terms effective force and effective closing force, as used in this application, are intended to be synonymous with the torque or moment which the resilient means 115, 116 exerts on the vane 110. Fig. 4 is a graph representing' a typical manner in which this effective closing foce exerted by the resilient means 1115, 116 on the vane varies as the vane moves from its closed to its fully-open position.

In its fully-open position the vane 110 bears against a suitable stop 121, which is so located that it lblocks opening movement of the vane prior to the crank arms 115 reaching a dead center position relative to the spring 116. As a result, the spring 116 still exerts a closing bias on the vane 110 lwhen the vane is fully open and is, accordingly, capable of restoring the vane to closed position when the pressure within the interrupter falls below a predetermined level.

A basic function of the exhaust valves 130 is to restrict the exhaust ports during those low current interruptions which generate relatively small quantities of gases. Without the valves, these gases would be dissipated so quickly through the large exhaust ports that no appreciable pressure build up would occur within the interrupter, which is a condition that would render interruption extremely difficult. A pump 30, soon to be described, is provided for pressurizing the iiuid within the interrupter during low current interruptions, but its effectiveness in this regard would be substantially impaired by the absence of any material downstream restriction in the exhaust ports, which would be the case if the valves 100 were not present. With the exhaust Ivalves 100 present, however, the arcing gases in cooperation with the pump 30 produce a pressure build-up which greatly aids in interrupting the low current arc.

When a high current arc is established within the interrupter 1, the arc generates sufiicient pressure to force each of the Valve members 11G` out of its closed position into its fully-open position. As a result of these high pressures, liquid is impelled at high velocity through the region of the arc and out of the open valve. high velocity flow which accompanies the interruption of high currents is effective to rapidly extinguish the high current arc, and the valves, in opening widely help to prevent excessive pressure rises within the interrupter,

For extreme high current interruptions, however, I have found that the valves even though they operate at exceptionally high speeds to open large low-impedance exhaust ports, are not able to limit the pressures within the interrupter to the desired levels. This problem has been overcome in the disclosed interrupter by providing the interrupter with a pressure-relief valve 150, shown in Fig. 1 at the top of the interrupter.

For reasons which will soon be explained in detail, this pressure-relief valve 150 is located at a point remote from any of the arcing regions of the interrupter. For example, in the disclosed interrupter, the pressure-relief valve 150 is located further away from the nearest of the interrupters arcing regions than is the case with the exhaust valves. In this regard, note that the pressure relief valve 150 is several times further from the arcing region between the upper contacts 10, 11 than is the upper exhaust valve 100.

The pressure-relief valve 150 comprises a tubular valve body 152 threaded, or otherwise secured, within an opening formed in the adapter 4 at the top of the interrupter. A pair of openings 153 are provided in the walls of the valve body to act as exhaust ports for fluid flowing through the tubular body when the valve is open. Flow through the valve is controlled by means of a movable valve element 154, which is urged into the closed position of Fig. 1 by resilient means, such as the compression spring 156. This compression spring preferably bears at its rear end upon a suitable stop secured to the This valve body 152. In its closed position, the valve element 154 is positioned against `a suitable annular valve seat i155 formed internally of the body 152 and contacts the liquid filling the interrupter. The valve element remains in this closed position until the pressure within the interrupter exceeds a predetermined value. this predetermined value drive the valve element away from its valve seat 155 against the opposition of the spring 156, thereby exposing the exhaust ports 153 and allowing fluid -to be expelled from the interrupter through the exhaust ports.

In accordance with my invention, this relief valve is adjusted to open at a relatively low pressure. This pressure should not substantially exceed the pressure level required to initiate opening of the exhaust valves 10) and, preferably, should be slightly lower than such pressure level. For example, in the disclosed interrupter, highly effective pressure-lirniting action, even on extreme .high current interruptions, has been obtained by setting the pressure-relief valve 150 for operation at about 60 p.s.i. and the exhaust valve 106 for operation at about p.s.i. Tests have shown that if the pressure relief valve 150 `is set for operation at a pressure greater than about 150 percent of the exhaust valve setting, then the pressure relief valve will have little significant effect in limiting the pressures developed within the interrupter during extreme high current interruptions.

The remote location of the pressure relief valve 150 relative to the arcing regions of the interrupter and the relatively low setting of the pressure-relief valve are cooperating factors which cause high-current arcs to eject substantially only liquid, and no significant amount'bf gas, through the relief valve during the early stages of arcing, e.g., the first and second half cycles of arcing.

As a result, any fiow taking place through the pressurerelief valve prior to opening of the exhaust valves is substantially only liquid, and comprises nosignificant amount of gas. The gases generated during this interval are thus retained within the interrupter and fill the volume made available by the liquid discharged through the relief valve. limiting cushion which acts to protect the interrupter on a succeeding half cycle when the highest pressures normally occur.

As soon as the interrupting operation for relatively high currents has been completed, a pump 30 operates to scavenge the interrupter 1 of any ionized gases remaining after the interruption so as to prepare the interrupter `for possible reclosure followed by another interruption. To this end, the pump 30 forces 4a flow of fresh insulating liquid through the arc extinguishing unit via the passageways 31 and 25, 26 and the exhaust valves 100, all in a manner soon to be described in greater detail.

The pump 30, which is structurally similar to a corresponding pump described in the aforementioned McBride patent, comprises a cylinder 32 suitably secured to the interrupter casing 5 and connected with the passageways 31 by means of ducts 43 and 43a. The pump 30 also comprises an impulse piston 3S which is spring biased downwardly by a compression spring 36. The compression spring 36 is mounted between a stationary part 37 and a stop 39 fixed to the piston rod 40, which in turn is fixed to the piston 35. The compression spring' 36 is held charged during the time the interrupter is closed by means of a plunger 39a fixed to the switch blade 2 andv abutting against the stop 39. However, when the switch blade 2 is driven downwardly to open the interrupter, the restraint of the plunger is removed and the spring 36 is free to begin driving the piston 35 downwardly against the opposition of the oil disposed therebeneath.

During high current interruptions the spring 36 is ineffective to produce substantial downward movement of the piston 35 until after the high current arcs are extinguished. This is the case because these high current arcs generate sufficient pressure to overcome the action Pressures above These retained gases form a pressure-- ofthe spring 36. It is only when these pressures subside that the pump becomes eiiective to impel liquid through the arc extinguishing unit.

For protecting the pump 3l) from high arc-generated pressures, the ducts 43 and 43a are preferably provided with check valves d4 and 44a disposed in the ducts 43 and 43a respectively. These check valves are adapted to cooperate with valve seats 45 and 45a respectively located within the ducts. The valves are free to slide on -their centrally disposed spindles 46 and 45a, which are supported from the valve seats by suitable spiders. These valves Vfreely permit liuid flow therethrough from the pump 30 except when the pressure produced by the arcs drawn by the contacts 1l an 1.3 predominates. Under such conditions, the. valves close automatically to protect the pump from objectionable arc-generated back pressures. The ability of a pump such as Sil to produce eiective scavenging action is dependent upon the particular paths through which the pump impels the fresh insulating liquid. In general, it is most desirable that the scavenging action take place through those particular passages which had been relied upon for the venting of gases during interruption, since it is here that the arcing gases are more likely to have been left behind or trapped. For example, in the disclosed interrupter it is particularly important that the exhaust passages 25 and 25 be etfectively freed of arcing products by the scavenging action. Any arcing gases in the region above the baille stack can be vented through small bleed holes such as i7@ provided at the top of the interruptor without the need for appreciable liquid ow in an upward direction. For these reasons, it is desirable that scavenging flow take place primarily through the exhaust passages 25, 26 and the exhaust valves i60, rather than through the pressure relief valve at the top of the interrupter. To assure that the scavenging action will follow this desired pattern, it is desirable that the pressure-relief valve 156 be closed and the exhaust valves 169 be opened during scavenging. This, of course, can be a problem if the pressure relief valve is setto open at a pressure below that required to initiate opening of an exhaust valve.

ln my interrupter, however, although pressure relief valve 150 might have a lower setting than the pressure required to initiate opening of the exhaust valves 10), l am still able to eiect scavenging in accordance with the desired pattern noted-above. To accomplish this result, advantage is taken of the fact that the pressure-relief valve has a positive gradient characteristic and the exhaust valve has a negative gradient characteristic. For example, assume that suiicient pressure has been generated within the interrupter during interruption to open both the pressure-relief valve l5@ and the exhaust valve 100. The negative gradient characteristic of the exhaust valve enables it to remain open after interruption and during scavenging because the pump Sil is capable of creating suicient pressure within the interrupter to hold the exhaust valve `in an open position during a major portion of the scavenging action. This pressure, however, is appreciably below the value required to hold the pressure-relief valve l open, and as a result the pressurerelief valve l closes and remains closed, thus allowing scavenging to occur with unimpaired effectivness through the exhaust passages 25, 26 and the exhaust valve 106'. Thus, by providing an exhaust valve which can be held open by pressures produced by the scavenging action of pump 3l), in combination with a pressure-relief valve lis extending through its valve ele- A ment 154. Flow through these bleed passages can occur freely while the valve element is closed. When the pressure within the interrupter exceeds a predetermined value, a slidable lia/p 172 biased away from the bleed passages 171 by spring 21H73 is forced into closed position relative to the bleed passages, thus providing additional area upon which pressure within the interruptor may act to force the valve element open if the pressure is suiiiciently high.

While l have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art thatvarious changes and modiiications may be made without departing from my invention in its broader aspects and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What i claim as new and desire to secure by Letters Patent of the `United States is:

l. In an electric circuit interrupter of lthe type that is normally lled with arc-extinguishing liquid, means for establishing an arc within said interrupter, an arcextinguishing baille structure including at least one exhaust passage leading to the exterior of said interrupter for venting arcing products from the region of said arc, a normally-closed exhaust valve located to restrict the ow of fluid through said exhaust passage and being arranged to open in response to pressures developed within said interruptor above a predetermined first value, a normally-closed pressure relief valve spaced from said arcextinguishing bar'iie structure for controlling iiuid flow from said interrupter, said pressure-relief valve being arranged to open prior to opening of said exhaust valve and in response to pressures developed within said interrupter lower than said irst value, said pressure-relief valve being normally in contact with the liquid filling said interrupter and being sufliciently remote from all arcing regions of said interrupter that any iiow therethrough prior to opening of said exhaust valve is substantially only liquid.

2. ln an electric circuit interrupter of the type that is normally filled with arc-extinguishing liquid, means for establishing an arc within said interruptor, arc-extinguishing baille structure including at least one exhaust passage leading to the exterior of said interrupter for venting arcing products from the region of said arc, a normallyclosed exhaust valve located to restrict the iiow of liuid through said exhaust passage and being arranged to open in response to pressures developed within said interrupter above a predetermined first value, a normallyclosed pressure relief valve spaced from all arc-extinguishing baille structure in said interrupter and adapted to control iluid ilow from said interrupter, said pressure relief valve being arranged to open prior to opening of said exhaust valve and whenever the pressures developed within said interrupter exceed a predetermined second value that is lower than said first value, said pressurerelief valve being located at a substantially greater distance from the nearest arcing region within said interrupter than is said exhaust valve.

3. In an electric circuit interrupter of the type that is normally filled with arc-extinguishing liquid, means `for establishing an arc within said interrupter, arc-extinguishing barile structure including at least one exhaust passage leading to the exterior of said interruptor for venting arcing products from the regio-n of said arc, a normallyclosed exhaust valve located to restrict the flow of liuid through said exhaust passage and being arranged to open in response to pressures developed within said interrupter above a predetermined iirst value, a Anormallyclosed pressure relief valve for said interrupter spaced from all arc-extinguishing baiile structure in said interrupter and being arranged to open in response to pressures developed within said iuterrupter above a predetermined second value that is not substantially greater than said lirst value and is substantially less than percent of said first value, said pressure-relief valve being suiciently remote from all arcing regions of said interrupter that any flow therethrough prior to opening of said exhaust valve is substantially only liquid.

4. The interrupter of claim 1 in combination with pump means operable after heavy current interruptions to pressurize fluid within said interrupter and to direct a flow of fluid through said arcing region and said exhaust passage, said exhaust valve being so constructed that it will be maintained open by pressures in the arcing l region of said interrupter substantially below the value required to initiate exhaust-valve-opening, operation of said pump means creating suiiicient pressure to hold said exhaust valve open in the event that said exhaust valve had been opened by a circuit-interrupting operation, operation of said pump means creating insufficient pressure when said exhaust valve is open to hold said pressure-relief valve open.

5. In an electric circuit interrupter adapted to `b iilled with arc-extinguishing liquid, means for establishing an arc within said interrupter, an arc-extinguishing baille structure including at least one exhaust passage leading to the exterior of said interrupter for venting arcing products from the region of said arc, a normallyclosed exhaust valve located to restrict the flow of iluid through said exhaust passage and being arranged to open in response to pressures developed within said interrupter above a predetermined lirst value, a normallyclosed pressure relief valve spaced from said arc-extinguishing bale structure for controlling fluid iow from said interrupter, said pressure-relief valve being arranged to open prior to opening of said exhaust valve and in response to pressures developed within said interrupter lower than said rst value, pump means operable after heavy current interruptions to pressurize fluid within said interrupter and to direct a ow of liuid through said arcing region andsaid exhaust passage, said exhaust valve being so constructed that it will be maintained open by pressures in the arcing region of said interrupter substantially below the value required to initiate exhaust-valve-opening, operation of said pump means creating suicient pressure to hold said exhaust valve open in the event that said exhaust valve had been opened by a circuit-interrupting operation, operation of said pump means creating insuicient pressure when said exhaust valve is open to hold said pressure-relief valve open.

6. The interrupter of claim 3 in combination with pump means operable after heavy current interruptions to pressurize uid within said interrupter and to direct a ow of fluid through said arcing region and said exhaust passage, said exhaust valve being so constructed that it will be maintained open by pressures in the arcing region of said interrupter substantially below the value required to initiate exhaust-valve-opening, operation of said pump means creating sulcient pressure to hold said References Cited in the tile of this patent UNITED STATES PATENTS 2,160,673 Prince May 30, 1939 2,647,973 Umphrey Aug. 4, 1953 2,749,412 McBride et al. June 5, 1956 2,806,111 Baker et a1. Sept. 10, 1957 

